第48回統計地震学セミナー / The 48th Statistical Seismology Seminar

Date&Time
2015年2月24日(火)
/ 24 February, 2015 (Tuesday) 16:00 –

Admission Free,No Booking Necessary

Place
統計数理研究所 セミナー室6 (A508)
/ Seminar room 6 (A508) @ The Institute of Statistical Mathematics
Speaker
Takeo Ishibe
(Earthquake Research Institute, the University of Tokyo)
Title
" Overview of Seismicity Changes in Inland Japan after the 2011 Tohoku-Oki Earthquake and Its Interpretation "
Abstract

In this presentation, I overview the widespread changes in seismicity rate and distribution of focal mechanism after the Tohoku-Oki earthquake (Mw9.0) and summarize the possible contributing factors. In Tohoku, westward from the Tohoku-Oki source, significant increases in seismicity rate were observed in N. and S. Akita, SW off Oga peninsula, and Yamagata/Fukushima and Ibaraki/Fukushima boundary regions as well as other surrounding areas. On the other hand, aftershock activities in the source regions of recent large earthquakes such as the 2008 Iwate-Miyagi earthquake have been suppressed. In Kanto, southwest of the Tohoku-Oki source, interplate earthquakes were typically activated, while belt-like seismicity along the western edge of slab-slab contact zone and shallow earthquakes in some areas were also activated.

The most plausible factor is the static changes in the Coulomb stress, which seems to be valid for retrospectively forecasting the changes in seismicity on some level, while some activated seismicity showed clear counter-evidence. Remotely triggered local events, whose origin times are well coincided with the arrivals of mainshock seismic waves, suggest that dynamic stress changes also contribute. Some swarm-like activities, showing temporal expansion of the focal area which is attributed to fluid diffusion, suggest that changes in pore fluid pressure should be another possible factor. The contribution of indirectly triggered earthquakes might be important in some regions because stress changes imparted by neighboring indirect aftershocks could be comparable with those from a distant mainshock. Postseisimc slip and viscoelastic effect would play an important role for long-term hazard assessments.